Method for the preservation of a machine element and use of an anionic liquid

ABSTRACT

A method for the preservation of a machine element, in which, after the production and before the installation and/or start-up of the machine element, a preservative is applied on the surface thereof, wherein an ionic liquid is used as a preservative is provided.

The present invention relates to a method for preserving a machine element, a preservative being applied to its surface after its manufacture and prior to the installation and/or start of operation of the machine element.

BACKGROUND

To prevent damage to a machine element, in particular a machine element made of a steel alloy, it is customary to use a preservative in post-manufacturing treatment of such machine elements to prevent corrosion.

In past years, a new damage phenomenon known as “white etching cracks” (WEC) has occurred in machine elements, in particular in rolling bearings. These cracks appear in metallographic images of damaged areas of machine elements, in particular in rolling bearing raceways. In practice, the occurrence of such white etching cracks has resulted in failure of large rolling bearings, such as those installed in wind power plants, for example, long before their statistical service life expectancy in some cases, resulting in substantial damages.

DE 10 2007 055 575 A1 describes how WEC is combatted by creating inherent compressive stresses in the area of the raceways; such inherent compressive stresses may be created by a material-removing machining process.

EP 2 123 779 A1 describes the manufacture of raceways and/or rolling bodies from a hardened steel having a carbon content between 0.4 and 0.8% by weight to increase the fatigue strength and reduce the risk of occurrence of white etching cracks.

To increase the robustness with respect to white etching cracks in a rolling bearing,

EP 2 573 195 A1 proposes that the surface of a rolling body or a raceway be manufactured from a modified material, whereby the rolling bearing is exposed to an elevated temperature for a certain period of time while the bearing surface is in contact with a chemical additive.

WO 2012/022601 A1 proposes a lubricant composition capable of reducing the friction torques of rolling bearings. The lubricant composition contains an ionic liquid.

A lubricant based on an ionic liquid is known from WO 2007/010845 A1.

Similarly, EP 2 022 840 A2 has already proposed using a lubricant containing an ionic liquid for parts of a wind power plant.

Use of an ionic liquid as a component of a lubricant for a bearing is already known from US 2009/0069204 A1 as well as from the publication WO 2005/035702 A1 and from Ye et al., Chem. Commun., 2001, 2244-2245.

Likewise, reference is made to the following publication: Uerdingen, M., 2010, Ionic Liquids as Lubricants, Handbook of Green Chemistry, 6:203-219.

SUMMARY OF THE INVENTION

It is already known in the prior art that a lubricant for a machine element, for example, a rolling bearing of a wind power plant may be mixed with an ionic liquid. However the amount required for this is high, thereby resulting in substantial costs. Use quantities of 0.5% by weight to 40% by weight in mixture with base oils are described in WO 2008/154998 A1. Furthermore, use of large amounts of ionic liquids as lubricant components has resulted in new problems, such as a previously unresearched toxicological effect. Furthermore, an adaptation of the ionic liquid to the lubricant used is necessary, so that a standard oil, which has been used in the past, must be replaced by a special oil, which is miscible with the ionic liquid.

The object of the present invention is therefore to provide a method for preserving a machine element by which the occurrence of white etching cracks is counteracted.

It is an object of the present invention to provide a method using an ionic liquid as a preservative.

Within the scope of the present invention, it has surprisingly been found that the occurrence of white etching cracks is already counteracted by using an ionic liquid as a preservative for a machine element such as a rolling bearing. According to the present invention, the ionic liquid is applied to the surface of the machine element after the machine element has been manufactured but before it has been installed or operation has been started.

After the installation or the start of operation of the machine element, it may be operated with a traditional lubricant, for example, a lubricating oil. The comparatively small amount of ionic liquid, which is applied as a preservative, results in the desired lengthening of the service life of the machine element. As part of test runs, it has been found that by using the ionic liquid as a preservative, the service life is increased by a factor of 4 before white etching cracks occur.

The method according to the present invention has the advantage that only a small amount of ionic liquid is needed, and it only preserves the surface of the machine element before the latter has been installed. After the installation, the amount of ionic liquid applied to the surface becomes mixed with the lubricant.

One variant of the method according to the present invention provides that the ionic liquid is used in pure form. In this embodiment of the present invention, only the surface of the machine element is provided with the ionic liquid as a preservative. Alternatively, it may be provided in the method according to the present invention that the ionic liquid is used as a preservative additive mixed with a lubricant. However, the preservative additive is not a lubricant additive but instead is a mixture of an ionic liquid and additional components. The lubricant is preferably the same lubricant which is used to lubricate the machine element in the installed state. In the case of a machine element designed as a rolling bearing, the lubricant may be a lubricating oil.

Particularly good applicability of the method according to the present invention is obtained when the ionic liquid has an oil or fat solubility of at least 0.3% by mass. Accordingly, an amount of ionic liquid on the order of at least 0.3% by weight, based on the mass of the lubricant, may be used, which is thus substantially below the salting-out limit. Due to the property of oil solubility or fat solubility, particularly good compatibility with traditional lubricants or additives is ensured. The method according to the present invention is also particularly suitable for non-fat-soluble ionic liquids, which are miscible with other base oils, such as polyalkylene glycol oils, for example. They must at least be oil soluble but not necessarily fat soluble.

According to a refinement of the present invention, quaternary ammonium ions and/or quaternary phosphonium ions and/or tertiary sulfur ions are used for the cationic portion of the ionic liquid.

Examples of suitable quaternary ammonium cations are described by formula (1)

[N(R¹)₄]⁺  (1)

where R¹ stands for, independently of one another, straight-chain or branched alkyl with 1 to 20 carbon atoms, where one or more non-vicinal and non-α-position carbon atoms may be replaced by —O— or cycloalkyl with 3 to 7 carbon atoms, which may be substituted with straight-chain or branched alkyl groups having 1 to 6 carbon atoms or the two R¹ substituents may also be joined in such a way that a monocyclic molecule is formed.

Examples of suitable quaternary phosphonium cations are described by formula (2)

[P(R²)₄]⁺  (2)

where R², independently of one another, denotes straight-chain or branched alkyl with 1 to 20 carbon atoms, wherein one or more non-vicinal and non-a-position carbon atoms may be replaced by -0- or cycloalkyl with 3 to 7 carbon atoms, which may be substituted with straight-chain or branched alkyl groups with 1 to 6 carbon atoms.

Examples of suitable tertiary sulfonium cations are described by formula (3)

[S(R³)₃]⁺  (3)

where R³ denotes, independently of one another, straight-chain or branched alkyl with 1 to 20 carbon atoms.

A straight-chain or branched alkyl group with 1 to 18 carbon atoms includes, for example, methyl, ethyl, isopropyl, propyl, butyl, sec-butyl or tert-butyl, also pentyl, 1-, 2- or 3-methylbutyl, 1,1-, 1,2- or 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl or n-octadecyl. A straight-chain or branched alkyl group with 1 to 20 carbon atoms therefore consists of the aforementioned alkyl groups with 1 to 18 carbon atoms plus n-nonadecyl or n-eicosyl. If no further details are given about the type of alkyl group, then it is a straight-chain alkyl group.

Cycloalkyl groups with 3 to 7 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl which may be substituted with straight-chain or branched alkyl groups with 1 to 6 carbon atoms, such as those described above.

The le and R² substituents in the cations of formula (1) or (2) may be the same or different. With cations of formula (1) all substituents le are preferably the same or three substituents le are the same and one substituent le is different. A preferred monocyclic cation of formula (1) is a pyrrolidinium cation, the remaining le substituents being either the same or different, as described above. In the case of cations of formula (2), all R² substituents are preferably the same, or three R² substituents are the same and one R² substituent is different.

R¹ and R² substituents are in particular preferably methyl, ethyl, 2-methoxyethyl, ethoxymethyl, 2-ethoxyethyl, isopropyl, 3-methoxypropyl, propyl, n-butyl, sec-butyl, n-pentyl, n-hexyl, n-octyl, n-decyl, n-dodecyl or n-tetradecyl.

R³ substituents in the cations of formula (3) may also be the same or different. In cations of formula (3), all R³ substituents are preferably the same and preferably denote a straight-chain or branched alkyl group with 1 to 8 carbon atoms.

Preferred quaternary ammonium cations according to the present invention include trimethyl(ethyl)ammonium, triethyl(methyl)ammonium, tripropyl(methyl)ammonium, tributyl(methyl)ammonium, tripentyl(methyl)ammonium, trihexyl(methyl)ammonium, triheptyl(methyl)ammonium, trioctyl(methyl)ammonium, trinonyl(methyl)ammonium, tridecyl(methyl)ammonium, tridodecyl(methyl)ammonium, trihexyl(ethyl)ammonium, ethyl(trioctyl)ammonium, propyl(dimethyl)ethylammonium, butyl(dimethyl)ethylammonium, methoxyethyl(dimethyl)ethylammonium, methoxyethyl(diethyl)methylammonium, methoxyethyl(dimethyl)propylammonium, ethoxyethyl(dimethyl)ethylammonium.

Preferred monocyclic quaternary ammonium cations according to the present invention include 1,1-dimethylpyrrolidinium, 1-methyl-1-ethylpyrrolidinium, 1-methyl-1-propylpyrrolidinium, 1-methyl-1-butylpyrrolidinium, 1-methyl-1-pentylpyrrolidinium, 1-methyl-1-hexylpyrrolidinium, 1-methyl-1-heptylpyrrolidinium, 1-methyl-1-octylpyrrolidinium, 1-methyl-1-nonylpyrroli dinium, 1-methyl-1-decylpyrroli dinium, 1,1-diethylpyrrolidinium, 1-ethyl-1-propylpyrrolidinium, 1-ethyl-1-butylpyrrolidinium, 1-ethyl-1-pentylpyrrolidinium, 1-ethyl-1-hexylpyrrolidinium, 1-ethyl-1-heptylpyrrolidinium, 1-ethyl-1-octylpyrrolidinium, 1-ethyl-1-nonylpyrroli dinium, 1-ethyl-1-decylpyrrolidinium, 1,1-dipropylpyrrolidinium, 1-propyl-1-methylpyrrolidinium, 1-propyl-1-butylpyrrolidinium, 1-propyl-1-pentylpyrrolidinium, 1-propyl-1-hexylpyrrolidinium, 1-propyl-1-heptylpyrrolidinium, 1-propyl-1-octylpyrrolidinium, 1-propyl-1-nonylpyrrolidinium, 1-propyl-1-decylpyrrolidinium, 1,1-dibutylpyrrolidinium, 1-butyl-1-methylpyrrolidinium, 1-butyl-1-pentylpyrrolidinium, 1-butyl-1-hexylpyrrolidinium, 1-butyl-1-heptylpyrrolidinium, 1-butyl-1-octylpyrrolidinium, 1-butyl-1-nonylpyrrolidinium, 1-butyl-1-decylpyrrolidinium, 1-butyl-1-dodecylpyrrolidinium, 1,1-dipentylpyrrolidinium, 1-pentyl-1-hexylpyrrolidinium, 1-pentyl-1-heptylpyrrolidinium, 1-pentyl-1-octylpyrrolidinium, 1-pentyl-1-nonylpyrrolidinium, 1-pentyl-1-decylpyrrolidinium, 1,1-dihexylpyrrolidinium, 1-hexyl-1-heptylpyrrolidinium, 1-hexyl-1-octylpyrrolidinium, 1-hexyl-1-nonylpyrrolidinium, 1-hexyl-1-decylpyrrolidinium, 1,1-dihexylpyrrolidinium, 1-hexyl-1-heptylpyrrolidinium, 1-hexyl-1-octylpyrrolidinium, 1-hexyl-1-nonylpyrrolidinium, 1-hexyl-1-decylpyrrolidinium, 1,1-diheptylpyrrolidinium, 1-heptyl-1-octylpyrrolidinium, 1-heptyl-1-nonylpyrrolidinium, 1-heptyl-1-decylpyrrolidinium, 1,1-dioctylpyrrolidinium, 1-octyl-1-nonylpyrrolidinium, 1-octyl-1-decylpyrrolidinium, 1-1-dinonylpyrrolidinium, 1-nonyl-1-decylpyrrolidinium or 1,1-didecylpyrrolidinium.

Particularly preferred quaternary ammonium cations according to the present invention include trioctyl(methyl)ammonium, tridodecyl(methyl)ammonium, 1-butyl-1-methylpyrrolidinium or 1-butyl-1-dodecylpyrrolidinium.

Exceptionally preferred quaternary ammonium cations according to the present invention are trioctyl(methyl)ammonium or tridodecyl(methyl)ammonium.

Preferred quaternary tetraalkylphosphonium cations according to the present invention are trimethyl(ethyl)phosphonium, triethyl(methyl)phosphonium, tripropyl(methyl)phosphonium, tributyl(methyl)phosphonium, tripentyl(methyl)phosphonium, trihexyl(methyl)phosphonium, triheptyl(methyl)phosphonium, trioctyl(methyl)phosphonium, trinonyl(methyl)phosphonium, tridecyl(methyl)phosphonium, trihexyl(ethyl)phosphonium, ethyl(trioctyl)phosphonium, propyl(dimethyl)ethylphosphonium, butyl(dimethyl)ethylphosphonium, methoxyethyl(dimethyl)ethylphosphonium, methoxyethyl(diethyl)methylphosphonium, methoxyethyl(dimethyl)propylphosphonium, ethoxyethyl(dimethyl)ethylphosphonium. Particularly preferred quaternary phosphonium cations are trihexyltetradecylphosphonium and/or trioctylmethylphosphonium.

Preferred tertiary sulfonium cations according to the present invention are trimethylsulfonium, triethylsulfonium, tripropylsulfonium, tributylsulfonium, trioctylsulfonium, tridodecylsulfonium.

It is also within the scope of the present invention that phosphate anions and/or borate anions and/or triflate anions and/or molybdate-containing anions and/or vanadate anions are used for the anionic portion of the ionic liquid. Alternatively or additionally, naphthalate anions may optionally also be used.

Examples of suitable phosphate anions include dimethyl phosphate, diethyl phosphate, dipropyl phosphate, dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, dioctyl phosphate or bis(2-ethylhexyl) phosphate.

Examples of suitable borate anions include tetracyanoborate, monofluorotricyanoborate, difluorodicyanoborate or tetrakis trifluoromethyl borate.

Phosphate anions as described above are preferred according to the present invention.

One particularly preferred phosphate anion is dimethyl phosphate.

According to a refinement of the present invention, a cation as described above or as described as preferred is selected for the cationic portion of the ionic liquid, and an anion as described above or as described as preferred is selected for the anionic portion of the ionic liquid.

Consequently, particularly preferred ionic liquids according to the present invention are trioctyl(methyl)ammonium dimethyl phosphate and tridodecyl(methyl)ammonium dimethyl phosphate.

The ionic liquids to be used according to the present invention are commercially available, for example, or may be prepared by processes familiar to those skilled in the art in the field of synthesis of ionic liquids.

The ionic liquids according to the present invention are preferably prepared by methods which avoid the use of chloride ions to rule out contamination of the ionic liquid with chloride ions. For the use according to the present invention, it is preferable that the ionic liquid not contain any chloride ions.

The preservative contains one or more halide-free ionic liquids or at least salts of the following basic structure:

[A]_(n) ^(m+)[X]_(k) ^(l−)

where k, l, m, n may assume the values 1, 2, 3 and 4; n and k stand only for the number of ions and not necessarily the same ions. Different anions or cations may thus be present in the ionic liquid.

[A]_(n) ^(m+) may stand for a sulfonium ion, an oxonium ion, a quaternary ammonium ion or a phosphonium ion. In addition, cation mixtures, multicationic ions, such as, for example, dications or trications and polyvalent cations, such as, for example, metal cations may also be used.

[X]_(k) ^(l−) stands for an anion, an anion mixture or a multianionic ion, such as, for example, ethylenediaminetetraacetate.

Preferred cations include in particular

the cyclic and noncyclic phosphonium ions of the general structures:

where R′, R″ and R″′ may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles having 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles having 4 to 14 hydrocarbon units; olefinic cycles and polycycles having 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles having 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, CSN, R—(CF₂)_(n)—CF₃, R—CF₃, R═CF₂.

Particularly preferred phosphonium cations having the previously defined radicals include quaternary phosphonium ions of the structure R″PR′₃ such as, for example, trihexyltetradecylphosphonium, trioctylmethylphosphonium, trihexylmethylphosphonium or tetrabutylphosphonium;

the cyclic and noncyclic ammonium ions of the general structures:

where R′, R″ and R″′ may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, CSN, R—(CF₂)_(n)—CF₃, R—CF₃, R═CF₂.

Especially preferred ammonium cations having the radicals defined previously include pyrrolidinium ions, pyridinium ions, imidazolium ions and quaternary ammonium ions of the R″NR′3 structure, such as, for example, trioctylmethylammonium, trimethylhexadecylammonium, trihexylmethylammonium or tetrabutylammonium;

the cyclic and noncyclic oxonium and sulfonium ions of the general structures:

where R′, R″ and R″′ may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, CSN, R—(CF₂)_(n)—CF₃, R—CF₃, R═CF₂.

Anions may contain halogens but not halides (Cl, Br, F and I).

Preferred anions are in particular

the cyclic and noncyclic phosphate, phosphonate and phosphinate anions of the general structures:

where R′ and R″ may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, CSN, R—(CF₂)_(n)—CF₃, R—CF₃, R═CF₂.

Particularly preferred phosphate, phosphonate and phosphinate anions having the previously defined radicals include phosphates such as, for example, bis(2-ethylhexyl)phosphate, dihexyl phosphate, dibutyl phosphate, diethyl phosphate, dimethyl phosphate, diethyldithio- phosphate and polyalkylene glycol phosphate; phosphonates, such as, for example, methylbutylphosphonate, methyloctylphosphonate and methylpolyalkylene glycol phosphonate; phosphinates such as, for example, bis(2,4,4-trimethylpentyl)phosphinate, diisobutyldithio-phosphinate, diisooctyldithiophosphinate and dibutylphosphinate;

the cyclic and noncyclic sulfate and sulfonate anions of the general structures

where R′ may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, CSN, R—(CF₂)_(n)—CF₃, R—CF₃, R═CF₂.

Particularly preferred sulfate and sulfonate anions having the previously defined radicals include sulfates such as, for example, dodecylsulfate, decylsulfate, octylsulfate, heptylsulfate, hexylsulfate, butylsulfate, ethylsulfate and methylsulfate; sulfonates such as, for example, dodecylsulfonate, decylsulfonate, octylsulfonate, heptylsulfonate, hexylsulfonate, butylsulfonate, ethylsulfonate, methylsulfonate, paratolylsulfonate and sodium dioctylsulfosuccinate;

the cyclic and noncyclic amide anions of the general structure

where R and R′ may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, R—CSN, R—SO₂—(CF₂)_(n)—CF₃, R—(CF₂)_(n)—CF₃, R—SO₂—CF₃, R—CF₃, R═CF₂.

Particularly preferred amide anions having the previously defined radicals include dicyanoamide, bis(trifluoromethylsulfonyl)amide and bis(pentafluoroethylsulfonyl)amide;

the cyclic and noncyclic carbene anions of the general structure

where R, R′ and R″ may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, R—CSN, R—SO₂—(CF₂)_(n)—CF₃, R—(CF₂)_(n)—CF₃, R—SO₂—CF₃, R—CF₃, R═CF₂.

Particularly preferred carbene anions having the previously defined radicals include tricyanomethide and carbenes of the Arduengo type;

the cyclic and noncyclic carboxylate anions of the general structure

where R may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, R—CSN, R—SO₂—(CF₂)_(n)—CF₃, R—(CF₂)_(n)—CF₃, R—SO₂—CF₃, R—CF₃, R═CF₂.

Particularly preferred carboxylate anions having the previously defined radicals include anions of carboxylic acids such as, for example, fatty acids; of the dicarboxylic acids such as sebacic and succinic acid; tetracarboxylic acids such as ethylenediaminetetraacetic acid;

the cyclic and noncyclic carbonate anions of the general structure

where R may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO₄—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, R—CSN, R—SO₂—(CF₂)_(n)—CF₃, R—(CF₂)_(n)—CF3, R—SO₂—CF₃, R—CF₃, R═CF_(2.)

Particularly preferred carbonate anions having the previously defined radicals include anions of carbonic acid such as methyl carbonate, ethyl carbonate and hydrocarbonate;

the cyclic and noncyclic carbonate anions of the general structures

where R, R′, R″ and R″′ may stand for the following radicals: hydrogen, straight-chain or branched alkyl chains with 1-20 carbon-hydrogen units; straight-chain or branched alkylene chains with 1-20 hydrocarbon units, where at least one double bond is present in the chain; straight-chain or branched alkyne radicals with 1-20 hydrocarbon units, where at least one triple bond is present in the chain; aromatics, substituted aromatics, heterocycles, substituted heterocycles, aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; substituted aliphatic cycles and polycycles with 4 to 14 hydrocarbon units; olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; substituted olefinic cycles and polycycles with 4 to 14 hydrocarbon units, where at least one double bond is present in the ring; polymer chains consisting of, for example, polyalkylene glycol, polyurethane and polyester units; chains or cycles of the radicals defined above with the following functional groups: R—O—R, R—OH, R—O—CO—R, R—NH—R, R—NH₂, R—SO₃—R, R—SO₂—R, R—SO4—R, R—SO—R, R—S—R, R—SH, R—N—CO—R, R—O—CO—OR, R—S—S—R, R—P—R, R—N═R, R—NR₂, R—CO—R, R—O—C—N(CH₃)₃, R—O—C—C(CH₃)₃, R—CN, R—CSN, R—SO₂-(CF₂)_(n)—CF₃, R—(CF₂)_(n)—CF₃, R—SO₂—CF₃, R—CF₃, R═CF₂.

Particularly preferred borate anions having the previously defined radicals include tetra(p-tolyl)borates and tetrakis(4-biphenylyl)borates;

- the transition metal anions particularly preferred transition metal anions contain vanadium, tungsten and molybdenum.

The method according to the present invention may be used particularly cost-efficiently when the amount of ionic liquid in the lubricant is approximately 0.3% to 10% by weight. It has been discovered that a greater amount of ionic liquid does not result in a longer service life of the machine elements, in particular the rolling bearings. The comparatively small amount of ionic liquid is therefore sufficient.

In addition the present invention relates to the use of an ionic liquid as a preservative for preserving a machine element by applying the ionic liquid to the surface of the machine element after it is manufactured and before it is installed and/or before the start of operation of the machine element.

Unlike the process known in the prior art, the ionic liquid is not used merely as an additive to a lubricant and instead it is used as a preservative additive which is applied immediately after manufacturing. The core of the present invention is thus the use of an essentially known ionic liquid for a new purpose.

DESCRIPTION OF ONE EXEMPLARY EMBODIMENT

One exemplary embodiment of the present invention is described in greater detail below.

A machine element manufactured from a steel alloy, namely a rolling bearing consisting of an outer ring, an inner ring and rolling bodies in the form of balls situated in between is preserved after being manufactured by applying an ionic liquid as a preservative to the surface of a rolling bearing. The ionic liquid used in this exemplary embodiment is trioctyl(methyl)ammonium dimethyl phosphate.

The ionic liquid is characterized in that between 0.3% and 10% by weight, it is fat or oil-soluble without salting out.

The process of preserving the machine element by applying the ionic liquid is carried out by the manufacturer after the machine element has been manufactured. In the preserved state, the machine element, in particular the rolling bearing, is delivered to a customer. In this exemplary embodiment the rolling bearing is used only to support a rotatable component of a wind power plant. In the installed state the rolling bearing is surrounded by a lubricating oil, possibly together with additional parts such as gear components. The ionic liquid applied to the surface of the rolling bearing becomes mixed with the lubricant which in this exemplary embodiment is a standard oil so that the ionic liquid is present in a low concentration in the lubricant during operation of the rolling bearing. This at least low concentration of the ionic liquid causes premature wear on the rolling bearing to be prevented, in particular in the area of the raceways or the rolling bodies. Tests have shown that the service life is increased by the method according to the present invention by a factor of 4 in comparison with machine elements in which no ionic liquid is used, as is to be expected. 

What is claimed is: 1-9. (canceled)
 10. A method for preserving a machine element comprising: applying a preservative to a surface of the machine element after manufacture and prior to installation or start of operation of the machine element, the preservative being an ionic liquid.
 11. The method as recited in claim 10 wherein the ionic liquid is used in pure form or as a preservative additive mixed with a lubricant.
 12. The method as recited in claim 10 wherein the ionic liquid has an oil or fat solubility of at least 0.3% by weight.
 13. The method as recited in claim 12 wherein the ionic liquid has an oil or fat solubility of up to 10% by weight.
 14. The method as recited in claim 10 wherein a cationic portion of the ionic liquid includes quaternary ammonium ions or quaternary phosphonium ions or tertiary sulfur ions.
 15. The method as recited in claim 10 wherein an anionic portion of the ionic liquid includes phosphate anions or borate anions or triflate anions or molybdate-containing anions or vanadate anions.
 16. The method as recited in claim 11 wherein the ionic liquid is used as the preservative additive and an amount of ionic liquid in the lubricant is approximately 0.3% to 10% by weight.
 17. A method for using ionic liquid as a preservative for a machine element comprising: applying the ionic liquid to a surface of the machine element after manufacture and prior to installation or start of operation of the machine element, the preservative being an ionic liquid.
 18. The method as recited in claim 17 wherein the ionic liquid is used in pure form or as a preservative additive mixed with a lubricant.
 19. The method as recited in claim 18 wherein the ionic liquid has an oil or fat solubility of at least 0.3% by weight.
 20. The method as recited in claim 19 wherein the ionic liquid has an oil or fat solubility of up to 10% by weight. 